Add codeowners to translation strings files. (#4992)

<!-- READ ME FIRST: Please fill in the explanation section below and
check off every point from the Essential Checklist! -->
## Explanation
Adding @adhiamboperes and me to codeowners so that we can help with
translation string file approvals (like #4969).

## Essential Checklist
<!-- Please tick the relevant boxes by putting an "x" in them. -->
- [ ] The PR title and explanation each start with "Fix #bugnum: " (If
this PR fixes part of an issue, prefix the title with "Fix part of
#bugnum: ...".)
- [x] Any changes to
[scripts/assets](https://github.com/oppia/oppia-android/tree/develop/scripts/assets)
files have their rationale included in the PR explanation.
- [x] The PR follows the [style
guide](https://github.com/oppia/oppia-android/wiki/Coding-style-guide).
- [x] The PR does not contain any unnecessary code changes from Android
Studio
([reference](https://github.com/oppia/oppia-android/wiki/Guidance-on-submitting-a-PR#undo-unnecessary-changes)).
- [x] The PR is made from a branch that's **not** called "develop" and
is up-to-date with "develop".
- [x] The PR is **assigned** to the appropriate reviewers
([reference](https://github.com/oppia/oppia-android/wiki/Guidance-on-submitting-a-PR#clarification-regarding-assignees-and-reviewers-section)).

Co-authored-by: Ben Henning <[email protected]>

.github/CODEOWNERS

@@ -59,7 +59,7 @@ gradlew.bat @BenHenning
 /utility/src/main/res/**/*.xml @BenHenning
 
 # App UI strings.
-/app/src/main/res/values*/strings.xml @BenHenning
+/app/src/main/res/values*/strings.xml @BenHenning @seanlip @adhiamboperes
 /app/src/main/res/values*/untranslated_strings.xml @BenHenning
 
 # Proguard configurations.